His linguistic ability and fluency in Japanese would prove to be assets as his career progressed, especially as World War II began in Europe.

On his first voyage to Japan he had met another young naval officer, Joseph J. Rochefort, assigned to the same duty.

One year to the day before the attack on Pearl Harbor, Layton became combat intelligence officer on the staff of Admiral Husband E. Kimmel, Commander-in-Chief of the United States Pacific Fleet, which had recently been moved from its base in San Diego, California, to Pearl Harbor — over the objections of Admiral James O. Richardson, whom Kimmel replaced.

Layton's book And I Was There: Pearl Harbor and Midway — Breaking the Secrets describes how Kimmel and his army counterpart at Pearl Harbor, General Walter C. Short, the commanders there, were scapegoats for failures by higher-ups in Washington, D.C. Layton blamed Admiral Richmond K. Turner in particular for monopolizing naval intelligence in Washington that would have alerted Kimmel and his staff to the imminence of attack and to the fact that Pearl Harbor could be a target of that attack.

[page needed] Layton's argument is detailed and comprehensive, but in general, he maintains that although Washington was reading the highest level Japanese diplomatic code, Purple, little of this was ever made available to the field commanders, other than to General Douglas MacArthur in the Philippines, who failed to act, not only on the Purple data, but even after he knew that Pearl Harbor had been attacked.

The diplomatic information that they were denied not only contained data about the imminence of war, but also included messages sent from Honolulu to Tokyo by Takeo Yoshikawa, the spy sent to observe and report daily on the exact positions of ships in the harbor, using a grid system that was obviously designed for the purpose of targeting torpedoes and bombs.

Those above Turner, including his boss, the Chief of Naval Operations, Admiral Harold Rainsford Stark, and even General George Marshall, also come in for blame, though some details are still missing from the official record.

In a speech to the National Cryptologic Museum Foundation,[3] Biard describes Layton as the sixth member of the five-member team (Joseph J. Rochefort, Joe Finnegan, Alva B. Lasswell, Wesley A. Wright, Thomas Dyer) who produced the information that was vital to winning the Battle of Midway, following the Battle of the Coral Sea.

Layton and I found many intelligence interests in common having almost nothing to do with Dungeon work, so I came to know him very well and to appreciate fully his tremendous contributions to our results.

)[citation needed] Layton remained on the staff of the Pacific Fleet until February 1945, followed by a three-year tour of duty as Commander of the U.S.

During this time, Admiral Chester W. Nimitz, as a mark of his recognition of Layton's contributions, invited him to Tokyo Bay when the Japanese formally surrendered on September 2, 1945.

His book, And I Was There: Pearl Harbor and Midway — Breaking the Secrets, was written with co-authors Roger Pineau and John Costello and was published in 1985, the year after Layton died.

The Navy/Marine Corps Intelligence Training Center in Dam Neck VA is named Layton Hall.